1. Field of the Invention
This invention relates to a spud for centering a filament in an incandescent lamp. More particularly, this invention relates to a spud for radially aligning a filament in a double ended tungsten halogen lamp wherein said spud is made of refractory metal wire in the shape of a circular ring having a loop on both sides of said ring which extend towards the center of the ring and with one of each of said wire ends extending out from a respective end of each loop, one end of which is attached to the filament and the other end being part of an inlead.
2. Background of the Disclosure
Double ended filament lamps comprising a generally tubular vitreous envelope enclosing a filament within and being hermetically sealed at both ends are well known to those skilled in the art. Such lamps include heat lamps which are generally made of a quartz tube enclosing an elongated tungsten filament supported along its length by one or more filament supports, with the tube hermetically sealed on both ends by means of a pinch seal over a molybdenum foil seal assembly. Heat lamps of this type do not generally require precise centering of the filament in the quartz tube. A relatively recent development is a double ended tungsten halogen lamp containing a tungsten filament and one or more halogens within the filament chamber, with the surface of the filament chamber containing a coating or filter which transmits visible light radiation, but which reflects infrared radiation back to the filament to decrease the amount of electrical power used by the lamp with no decrease in visible light output. Such lamps require precise radial alignment of the filament along the optical center of the filament chamber in order to achieve maximum conversion of the infrared radiation reflected by the coating back to the filament to visible light radiation which is transmitted by the filter.
Thin film optical interference filters for reflecting infrared radiation emitted by a filament back to the filament while at the same time transmitting the visible light portion of the electromagnetic spectrum emitted by the filament and their applications as coatings on lamps are known to those skilled in the art and may be found, for example, in U.S. Pat. Nos. 4,017,758; 4,652,789; 4,663,557 and 4,701,663. For example, it is known that light interference filters made up of alternating layers of tantala and silica may be employed on the outer surface of a vitreous filament chamber for selectively reflecting infrared radiation emitted by the filament back to the filament and which preferentially transmits radiation in the visible portion of the electromagnetic spectrum. In these types of filters the infrared radiation is reflected by the filter or coating back to the filament wherein at least a portion is reconverted to light radiation in the visible portion of the electromagnetic spectrum, thereby greatly increasing the efficacy of the lamp and, at the same time, reducing the amount of heat emitted by the lamp. In those applications wherein it is desired to reflect at least a portion of the infrared radiation emitted by the filament back to the filament for conversion into visible light radiation, it is important that the filament be fairly precisely centered or aligned along the optical axis of the filament chamber in order for the filter to work effectively. That is, if the filament isn't at the optical center of the coated filament chamber, then a substantial portion of the infrared radiation reflected by the filter will miss the filament and strike the wall on the other side of the chamber. As a practical matter, all coatings or filters that reflect infrared radiation also transmit a small fraction of the radiation striking the filter. Accordingly, a portion of the infrared radiation is transmitted by the filter at each reflection. Thus, a substantial portion of infrared radiation which undergoes multiple reflections before encountering the filament can be lost through the filter before being converted into visible light radiation.
Single ended tungsten halogen incandescent lamps comprising a vitreous envelope made out of quartz or a suitable high temperature glass, such as an aluminosilicate glass, which enclose a tungsten filament along with one or more halogen compounds and a getter such as phosphorus or phosphine in the filament chamber are also well known to those skilled in the art. Such lamps are disclosed, for example, in U.S. Pat. Nos. 3,712,701; 4,629,935; 4,629,936. In these lamps the tungsten filament is mounted axially along the length of the lamp within the vitreous lamp envelope by inleads which are hermetically sealed in the end of the lamp. In these types of lamps, employing an infrared reflective coating around the envelope or filament chamber is not normally effective, because it is difficult to radially align the filament along the optical center of the envelope. Furthermore, the construction of single ended tungsten halogen lamps makes it extremely difficult to shape the ends of the vitreous envelope so that the reflected radiation is returned to the filament with a minimum number of reflections. For these reasons increasing attention has been given to constructing double ended tungsten halogen lamps which comprise a vitreous envelope having a bulbous filament chamber and terminating at both ends in tubular portions. Such lamps are disclosed, for example, in U.S. Pat. No. 4,810,932 the disclosures of which are incorporated herein by reference. However, there still remains a need for precisely centering or radially aligning the tungsten filament within the vitreous envelope.